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9 Oct 2006

Volume 89, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 151920 (2006); http://dx.doi.org/10.1063/1.2360906 (3 pages)

Aycan Yurtsever, Matthew Weyland, and David A. Muller
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Optimum laser pulse duration for efficient extreme ultraviolet light generation from laser-produced tin plasmas

Tsuyoshi Ando, Shinsuke Fujioka, Hiroaki Nishimura, Nobuyoshi Ueda, Yuzuri Yasuda, Keiji Nagai, Takayoshi Norimatsu, Masakatsu Murakami, Katsunobu Nishihara, Noriaki Miyanaga, Yasukazu Izawa, Kunioki Mima, and Atsushi Sunahara

Appl. Phys. Lett. 89, 151501 (2006); http://dx.doi.org/10.1063/1.2361260 (3 pages) | Cited 23 times

Online Publication Date: 11 October 2006

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Conversion efficiencies (CEs) from incident laser energy to 13.5 nm light within a 2% bandwidth were measured with changing laser pulse durations for laser-produced tin plasmas. Experimental results indicate that the optimum pulse duration is determined by two parameters: one is the optical depth of tin plasma for 13.5 nm light and the other is laser absorption rate in 13.5 nm emission-dominant region. The maximum CE of 2.2% is obtained with pulse duration of 2.3 ns.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
42.72.Bj Visible and ultraviolet sources
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Strong configurational dependence of elastic properties for a binary model metallic glass

Gang Duan, Mary Laura Lind, Marios D. Demetriou, William L. Johnson, William A. Goddard, Tahir Çaģin, and Konrad Samwer

Appl. Phys. Lett. 89, 151901 (2006); http://dx.doi.org/10.1063/1.2360203 (3 pages) | Cited 26 times

Online Publication Date: 9 October 2006

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In this work, the strong dependence of elastic properties on configurational changes in a Cu–Zr binary metallic glass assessed by molecular dynamics simulations is reported. By directly evaluating the temperature dependence and configurational potential energy dependence of elastic constants, the shear modulus dependence on the specific configurational inherent state of metallic glasses is shown to be much stronger than the dependence on Debye-Grüneisen thermal expansion.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
61.43.Fs Glasses
61.43.Bn Structural modeling: serial-addition models, computer simulation
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Thermal quenching of photoluminescence from InAs/In0.53Ga0.23Al0.24As/InP quantum dashes with different sizes

P. Podemski, R. Kudrawiec, J. Misiewicz, A. Somers, R. Schwertberger, J. P. Reithmaier, and A. Forchel

Appl. Phys. Lett. 89, 151902 (2006); http://dx.doi.org/10.1063/1.2358312 (3 pages) | Cited 7 times

Online Publication Date: 9 October 2006

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InAs/In0.53Ga0.23Al0.24As quantum dashes (QDashes) have been investigated in a temperature-dependent photoluminescence (PL) experiment. It has been observed that the increase of the QDash size shifts the emission peak to the longer wavelength and leads to a slower thermal quenching of PL. This thermal quenching can be described by a standard expression with two characteristic activation energies which are attributed to the electron escape and the heavy-hole escape to the conduction and valence continua in QDash barriers, respectively. The found activation energies are in the range of 21–64 and 121–223 meV for the first and the second quenching mechanism, respectively.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)

Erbium-doped GaN epilayers synthesized by metal-organic chemical vapor deposition

C. Ugolini, N. Nepal, J. Y. Lin, H. X. Jiang, and J. M. Zavada

Appl. Phys. Lett. 89, 151903 (2006); http://dx.doi.org/10.1063/1.2361196 (3 pages) | Cited 19 times

Online Publication Date: 9 October 2006

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The authors report on the synthesis of Er-doped GaN epilayers by in situ doping by metal-organic chemical vapor deposition (MOCVD). The optical and electrical properties of the Er-doped GaN epilayers were studied by photoluminescence (PL) spectroscopy and van der Pauw–Hall method. Both above and below band gap excitation results in a sharp PL emission peak at 1.54 μm. In contrary to other growth methods, MOCVD grown Er-doped GaN epilayers exhibit virtually no visible emission lines. A small thermal quenching effect, with only a 20% decrease in the integrated intensity of the 1.54 μm PL emission, occurred between 10 and 300 K. It was found that Er incorporation has very little effect on the electrical conductivity of the GaN epilayers and Er-doped layers retain similar electrical properties as those of undoped GaN.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.55.A- Nucleation and growth

Thermal conductivity of phase-change material Ge2Sb2Te5

Ho-Ki Lyeo, David G. Cahill, Bong-Sub Lee, John R. Abelson, Min-Ho Kwon, Ki-Bum Kim, Stephen G. Bishop, and Byung-ki Cheong

Appl. Phys. Lett. 89, 151904 (2006); http://dx.doi.org/10.1063/1.2359354 (3 pages) | Cited 47 times

Online Publication Date: 10 October 2006

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The thermal conductivity of thin films of the phase-change material Ge2Sb2Te5 is measured in the temperature range of 27 °C<T<400 °C using time-domain thermoreflectance. From the low thermal conductivity of amorphous phase, the conductivity increases irreversibly with increasing temperature and undergoes large changes with phase transformations. Thermal transport in the amorphous and early cubic phases can be described by a random walk of vibrational energy, i.e., the minimum thermal conductivity. In the hexagonal phase, the electronic contribution to the thermal conductivity is larger than the lattice contribution. Crystallization by laser processing produces a cubic phase with a lower thermal conductivity than cubic phases produced by thermal annealing; the authors attribute this difference in conductivity to a larger degree of atomic-scale disorder in films that are crystallized on short time scales.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
64.70.K- Solid-solid transitions
73.61.Le Other inorganic semiconductors

Defect structure in micropillars using x-ray microdiffraction

R. Maaβ, D. Grolimund, S. Van Petegem, M. Willimann, M. Jensen, H. Van Swygenhoven, T. Lehnert, M. A. M. Gijs, C. A. Volkert, E. T. Lilleodden, and R. Schwaiger

Appl. Phys. Lett. 89, 151905 (2006); http://dx.doi.org/10.1063/1.2358204 (3 pages) | Cited 31 times

Online Publication Date: 11 October 2006

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White beam x-ray microdiffraction is used to investigate the microstructure of micron-sized Si, Au, and Al pillars fabricated by focused ion beam (FIB) machining. Comparison with a Laue pattern obtained from a Si pillar made by reactive ion etching reveals that the FIB damages the Si structure. The Laue reflections obtained from the metallic pillars fabricated by FIB show continuous and discontinuous streakings, demonstrating the presence of strain gradients.
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61.72.Dd Experimental determination of defects by diffraction and scattering
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Effects of the material polarity on the green emission properties of InGaN/GaN multiple quantum wells

Yen-Lin Lai, Chuan-Pu Liu, Yung-Hsiang Lin, Ray-Ming Lin, Dong-Yuan Lyu, Zhao-Xiang Peng, and Tai-Yuan Lin

Appl. Phys. Lett. 89, 151906 (2006); http://dx.doi.org/10.1063/1.2360247 (3 pages) | Cited 10 times

Online Publication Date: 11 October 2006

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Green-light-emission InGaN/GaN multiple quantum wells (MQWs) with different polarities were grown by metal organic chemical vapor deposition. A clear phase separation was observed both in the Ga- and N-polarity samples by high resolution transmission electron microscopy, corresponding to two InGaN-related emissions (In-rich dots and an InGaN matrix) seen in photoluminescence spectra. The dot-related emission in the Ga-polarity MQWs shows stronger carrier localization, as well as a weak influence of defects and temperature insensitivity, when compared to the N-polarity MQWs. In addition, efficient carrier transport, from the low-indium InGaN matrix to high-indium In-rich dots, was observed in the Ga-polarity structure, enhancing the function of quantum-dot structures with Ga polarity, and resulting in a high quantum yield of green light emission.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
73.63.Hs Quantum wells
72.20.Fr Low-field transport and mobility; piezoresistance
64.75.-g Phase equilibria

Arbitrary surface structuring of amorphous silicon films based on femtosecond-laser-induced crystallization

Geon Joon Lee, Seok Ho Song, YoungPak Lee, Hyeonsik Cheong, Chong Seung Yoon, Yong Duck Son, and Jin Jang

Appl. Phys. Lett. 89, 151907 (2006); http://dx.doi.org/10.1063/1.2358922 (3 pages) | Cited 9 times

Online Publication Date: 11 October 2006

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The arbitrary surface structuring of amorphous silicon (a-Si) films was performed by applying the Fourier-transform (FT) method to the femtosecond-laser-induced crystallization. In order to realize the arbitrary structuring, the logo q-Psi was produced in the a-Si film by the FT of a computer-generated hologram. The crystallization of a-Si was performed using the near-infrared femtosecond-laser pulses. By micro-Raman spectroscopy, scanning-electron microscopy, and transmission-electron microscopy, it was found that the femtosecond-laser pulses induced a localized phase transformation from the amorphous to the crystalline phase, and the spatially selected crystallization of the a-Si was responsible for the formation of the two-dimensional pattern.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
68.47.Fg Semiconductor surfaces
81.65.-b Surface treatments
78.47.-p Spectroscopy of solid state dynamics
78.66.Db Elemental semiconductors and insulators

Optical properties of cubic Ti3N4, Zr3N4, and Hf3N4

Ming Xu, Songyou Wang, Gang Yin, Jing Li, Yuxiang Zheng, Liangyao Chen, and Yu Jia

Appl. Phys. Lett. 89, 151908 (2006); http://dx.doi.org/10.1063/1.2360937 (3 pages) | Cited 21 times

Online Publication Date: 11 October 2006

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A systematic theoretical study is presented for the electronic, mechanical, and optical properties of cubic Ti3N4, Zr3N4, and Hf3N4 with the Th3P4 structure in the framework of density functional theory. The calculated band structures of Ti3N4, Zr3N4, and Hf3N4 show the indirect band gaps of 0.268, 0.909, and 1.00 eV, respectively. Furthermore, the optical properties for all three materials were calculated and analyzed in detail. The calculated results are well consistent with available experimental data. Also, it is shown that all these materials have relatively large static dielectric constants at zero frequency, rendering them potential applications in microelectronic devices.
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71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
77.22.Ch Permittivity (dielectric function)
78.20.-e Optical properties of bulk materials and thin films

Band gap properties of Zn1−xCdxO alloys grown by molecular-beam epitaxy

X. J. Wang, I. A. Buyanova, W. M. Chen, M. Izadifard, S. Rawal, D. P. Norton, S. J. Pearton, A. Osinsky, J. W. Dong, and Amir Dabiran

Appl. Phys. Lett. 89, 151909 (2006); http://dx.doi.org/10.1063/1.2361081 (3 pages) | Cited 24 times

Online Publication Date: 11 October 2006

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Optical absorption and reflectance measurements are performed to evaluate compositional and temperature dependences of band gap energies of Zn1−xCdxO alloys grown by molecular-beam epitaxy. The compositional dependence of the band gap energy, determined by taking into account excitonic contributions, is shown to follow the trend Eg(x) = 3.37−2.82x+0.95x2. Incorporation of Cd was also shown to somewhat slow down thermal variation of the band gap energies, beneficial for future device applications.
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81.05.Dz II-VI semiconductors
71.20.Nr Semiconductor compounds
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.40.Fy Semiconductors

Polarized photoluminescence and absorption in A-plane InN films

Jayeeta Bhattacharyya, Sandip Ghosh, M. R. Gokhale, B. M. Arora, Hai Lu, and W. J. Schaff

Appl. Phys. Lett. 89, 151910 (2006); http://dx.doi.org/10.1063/1.2361174 (3 pages) | Cited 19 times

Online Publication Date: 11 October 2006

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The authors report the observation of strong polarization anisotropy in the photoluminescence (PL) and the absorption spectra of [11math0] oriented A-plane wurtzite InN films grown on R-plane (1math02) sapphire substrates using molecular beam epitaxy. For A-plane films the c axis lies in the film plane. The PL signal collected along [11math0] with electric vector E⊥c is more than three times larger than for E‖c. Both PL signals peak around 0.67 eV at 10 K. The absorption edge for E‖c is shifted to higher energy by 20 meV relative to E⊥c. Optical polarization anisotropy in wurtzite nitrides originates from their valence band structure which can be significantly modified by strain in the film. The authors explain the observed polarization anisotropy by comparison with electronic band structure calculations that take into account anisotropic in-plane strain in the films. The results suggest that wurtzite InN has a narrow band gap close to 0.7 eV at 10 K.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds

Chalcopyrite polymorph for superhard BC2N

Jian Sun, Xiang-Feng Zhou, Guang-Rui Qian, Jing Chen, Ya-Xian Fan, Hui-Tian Wang, Xiaoju Guo, Julong He, Zhongyuan Liu, and Yongjun Tian

Appl. Phys. Lett. 89, 151911 (2006); http://dx.doi.org/10.1063/1.2361267 (3 pages) | Cited 15 times

Online Publication Date: 11 October 2006

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A chalcopyrite structure is predicted for the potential superhard boron-carbonitride (BC2N), based on ab initio pseudopotential density functional method. Lattice constant, formation energy, bulk modulus, band structure, and electron density of states are calculated. The results show that this compound is a wide gap semiconductor with a direct band gap of about 3.3 eV. The calculated Vickers hardness is about 72 GPa, which is very close to the measured hardness of c-BC2N (76±4 GPa).
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81.05.Hd Other semiconductors
61.66.Fn Inorganic compounds
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Investigation of electronic structures of ordered and disordered Ni3Fe by electron energy loss spectroscopy

X. Y. Zhong, Jing Zhu, A. H. Zhang, and S. C. Mou

Appl. Phys. Lett. 89, 151912 (2006); http://dx.doi.org/10.1063/1.2357028 (3 pages) | Cited 3 times

Online Publication Date: 12 October 2006

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The electronic structures of ordered and disordered Ni3Fe have been investigated by electron energy loss spectroscopy. The threshold energies of the L2,3 edges of Fe, and then Ni, are different in the two phases and the white-line ratios L3/L2 of Ni and Fe from ordered Ni3Fe are lower than those from disordered Ni3Fe, while the 3d occupancies of Ni and Fe atoms in ordered Ni3Fe are less than those in disordered Ni3Fe. The s-p-d rehybridization and the intraband redistribution of the d-band electrons of Ni and Fe atoms are suggested to explain the authors’ experimental results.
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71.20.Be Transition metals and alloys
79.20.Uv Electron energy loss spectroscopy

Quantitative x-ray phase-contrast imaging of air-assisted water sprays with high Weber numbers

Y. J. Wang, Kyoung-Su Im, K. Fezzaa, W. K. Lee, Jin Wang, P. Micheli, and C. Laub

Appl. Phys. Lett. 89, 151913 (2006); http://dx.doi.org/10.1063/1.2358322 (3 pages) | Cited 7 times

Online Publication Date: 12 October 2006

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X-ray in-line phase-contrast imaging along with a single-image phase retrieval reconstruction was used to visualize the near-nozzle breakup of optically dense water jets atomized by a high-speed, annular air flow. The influence of the atomizing air on water mass distribution was investigated to reveal the complex air/liquid interactions at various breakup stages. Unlike low-Weber-number jets, the breakup of high-Weber-number jets can occur in the liquid core, which causes sudden decreases in liquid volume fraction.
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47.80.Jk Flow visualization and imaging
47.15.Uv Laminar jets
47.55.Ca Gas/liquid flows
47.15.Rq Laminar flows in cavities, channels, ducts, and conduits
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.85.Np Fluidics

Excitonic transfer in coupled InGaAs/GaAs quantum well to InAs quantum dots

Yu. I. Mazur, B. L. Liang, Zh. M. Wang, D. Guzun, G. J. Salamo, Z. Ya. Zhuchenko, and G. G. Tarasov

Appl. Phys. Lett. 89, 151914 (2006); http://dx.doi.org/10.1063/1.2360914 (3 pages) | Cited 14 times

Online Publication Date: 12 October 2006

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Peculiar mechanism of carrier transfer, excitonic trapping, from quantum well (QW) states to quantum dot (QD) states is clearly observed for the intentionally designed strained InAs:In0.3Ga0.7As/GaAs QD:QW structure. This transfer occurs very efficient at low excitation densities and low temperatures and explains the excitation density and nonmonotonic temperature dependences of the QW photoluminescence.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena

Structural investigation of CuIn5Se8 single crystals by optical second harmonic generation, ellipsometry, and photoluminescence

L. Kulyuk, V. Mirovitskii, E. Arushanov, V. Tezlevan, M. Leon, E. Mishina, N. Sherstyuk, T. Dumouchel, E. Fortin, and Th. Rasing

Appl. Phys. Lett. 89, 151915 (2006); http://dx.doi.org/10.1063/1.2362578 (3 pages) | Cited 2 times

Online Publication Date: 13 October 2006

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CuIn5Se8 bulk single crystals were characterized using ellipsometry, photoluminescence (PL), and optical second harmonic generation (SHG). The refractive n(E) and absorption k(E) indices as functions of photon energy E are determined. The structure of the PL spectrum suggests the presence of the Cu-rich nonstoichiometric phases at the natural surfaces of the CuIn5Se8 sample. The best fit of the experimental SHG data is achieved by assuming that CuIn5Se8 belongs to the math2m symmetry group. This result is in contradiction with x-ray analysis (math2m group), which testifies to the difference in surface and bulk structure.
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78.55.Hx Other solid inorganic materials
61.66.Fn Inorganic compounds
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Effects of compressive strain on optical properties of InxGa1−xN/GaN quantum wells

N. Khan and J. Li

Appl. Phys. Lett. 89, 151916 (2006); http://dx.doi.org/10.1063/1.2362587 (3 pages) | Cited 13 times

Online Publication Date: 13 October 2006

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In0.2Ga0.8N/GaN multiple quantum well (MQW) blue light emitting diode (LED) structure was grown on a specially designed sapphire substrate (with increasing thickness from the edge to the center within a single wafer). X-ray diffraction revealed that the GaN lattice constant c decreases continuously from the edge to the center, indicating a continuous variation in the compressive strain. The spectral peak positions of the electroluminescence (EL) spectra exhibited a blueshift when probed at the edge as compared to the center, which is a direct consequence of the continuous variation in the compressive strain across the wafer. Based on the experimental results, a ratio of elastic stiffness constants (C33/C13) for GaN was deduced to be ∼ 5.0±1.0, which was in agreement with the calculated value of ∼ 4.0. A linear relation of the EL emission peak position of LEDs with the biaxial strain was observed, and a linear coefficient of 19 meV/GPa characterizing the relationship between the band gap energy and biaxial stress of In0.2Ga0.8N/GaN MQWs was also obtained.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Oxygen atoms on Si(100)-(2×1): Imaging with scanning tunneling microscopy

B. R. Trenhaile, Abhishek Agrawal, and J. H. Weaver

Appl. Phys. Lett. 89, 151917 (2006); http://dx.doi.org/10.1063/1.2362623 (3 pages) | Cited 10 times

Online Publication Date: 13 October 2006

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The authors use scanning tunneling microscopy to study the initial stage of oxidation for H2O exposed Si(100). Following H2O dissociation and saturation of the surface with Cl, a mild anneal allows the oxygen to insert into the Si dimer bonds. Bridge-bonded oxygen atoms appear as a dark spot in the center of the dimer. The density of these “split dimer” defects correlates with the c-type defect density on the clean surface. These results also show how to produce nearly defect-free halogen-terminated Si(100).
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68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing

Competition between damage buildup and dynamic annealing in ion implantation into Ge

M. Posselt, L. Bischoff, D. Grambole, and F. Herrmann

Appl. Phys. Lett. 89, 151918 (2006); http://dx.doi.org/10.1063/1.2360238 (3 pages) | Cited 15 times

Online Publication Date: 13 October 2006

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Channeling implantation of Ga into Ge is performed at two very different ion fluxes (1012 and 1019 cm−2 s−1), at two temperatures (room temperature and 250 °C), and at five different fluences. The fluence dependence of the range profiles and of the implantation damage is strongly influenced by defect accumulation and dynamic annealing. At 250 °C, the maximum lifetime of the defects is less than 10 s. On the other hand, at room temperature no significant annealing is found within the first 10 s after ion impact. The measured Ga depth profiles are reproduced very well by atomistic computer simulations.
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81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing
61.72.S- Impurities in crystals

In situ transmission electron microscopy observations of 1.8 μm and 180 nm Cu interconnects under thermal stresses

J. H. An and P. J. Ferreira

Appl. Phys. Lett. 89, 151919 (2006); http://dx.doi.org/10.1063/1.2360240 (3 pages) | Cited 10 times

Online Publication Date: 13 October 2006

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In situ heating transmission electron microscopy was used to observe the stress relaxation behavior in 1.8 μm and 180 nm wide Cu interconnects in real time. 1.8 μm lines exhibit dislocation nucleation at the grain boundaries, while void nucleation/growth was observed in the 180 nm lines. The difference in the stress relaxation mechanism is due to distinct stress states among the two lines, namely, biaxial for the 1.8 μm lines and quasihydrostatic stress for the 180 nm lines. Quasihydrostatic stresses in the 180 nm lines are likely to lead to an absence of dislocation motion.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Three-dimensional imaging of nonspherical silicon nanoparticles embedded in silicon oxide by plasmon tomography

Aycan Yurtsever, Matthew Weyland, and David A. Muller

Appl. Phys. Lett. 89, 151920 (2006); http://dx.doi.org/10.1063/1.2360906 (3 pages) | Cited 28 times

Online Publication Date: 13 October 2006

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Silicon nanoparticles embedded in silica show promising optoelectronic properties, due to quantum confinement and/or radiative interface states that should correlate with the particles’ average size and shape. Here the authors report the combination of electron tomography with plasmon-filtered microscopy in order to reconstruct the three-dimensional morphology of silicon nanoparticles. They find that particles with complex morphologies and high surface to volume ratios are dominant, rather than the commonly assumed near-spherical structures. These results should affect quantum-confined excitons and the interface density of states. Their findings may help to explain the physical origin of the unusually broad photoluminescence bands and efficiencies.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
71.20.Mq Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.35.-y Excitons and related phenomena
73.20.At Surface states, band structure, electron density of states
78.55.Ap Elemental semiconductors

Transition between wurtzite and zinc-blende GaN: An effect of deposition condition of molecular-beam epitaxy

B. M. Shi, M. H. Xie, H. S. Wu, N. Wang, and S. Y. Tong

Appl. Phys. Lett. 89, 151921 (2006); http://dx.doi.org/10.1063/1.2360916 (3 pages) | Cited 13 times

Online Publication Date: 13 October 2006

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GaN exists in both wurtzite and zinc-blende phases and the growths of the two on its (0001) or (111) surfaces are achieved by choosing proper deposition conditions of molecular-beam epitaxy (MBE). At low substrate temperatures but high gallium fluxes, metastable zinc-blende GaN films are obtained, whereas at high temperatures and/or using high nitrogen fluxes, equilibrium wurtzite phase GaN epilayers resulted. This dependence of crystal structure on substrate temperature and source flux is not affected by deposition rate. Rather, the initial stage nucleation kinetics plays a primary role in determining the crystallographic structures of epitaxial GaN by MBE.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
64.70.K- Solid-solid transitions

Ion cutting and transfer of sub-100-nm silicon layers using low-keV H, D, and He ions

Nicholas Desrosiers and Bernard Terreault

Appl. Phys. Lett. 89, 151922 (2006); http://dx.doi.org/10.1063/1.2361182 (3 pages) | Cited 3 times

Online Publication Date: 13 October 2006

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The authors have investigated the ion cutting and transfer of silicon layers thinner than 100 nm using 5–8 keV H, D, or He ions. The thickness and morphology of the transferred layers have been characterized as a function of ion fluence. Ion cutting of bonded layers occurs in a much wider fluence range than blistering of free surfaces. The optimal surface roughness (2 nm) is obtained with rather high H or D doses of (7–8)×1016 at./cm2, although the threshold dose is 1.5×1016 H/cm2 only. These results demonstrate the importance of the boundary conditions imposed on the splitting process by the bonded wafer.
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61.80.Jh Ion radiation effects
68.47.Fg Semiconductor surfaces

Variable core model and the Peierls stress for the mixed (screw-edge) dislocation

Vlado A. Lubarda and Xanthippi Markenscoff

Appl. Phys. Lett. 89, 151923 (2006); http://dx.doi.org/10.1063/1.2361277 (3 pages) | Cited 4 times

Online Publication Date: 13 October 2006

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A variable core model of a moving crystal dislocation is proposed and used to derive an expression for the Peierls stress. The dislocation width varies periodically as a dislocation moves through the lattice, which leads to an expression for the Peierls stress in terms of the difference of the total energies in the crystal corresponding to stable and unstable equilibrium configurations of the dislocation, rather than the difference in the misfit energies alone. Results for both edge and mixed dislocations are given and proposed to be used in conjunction with ab initio calculations.
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61.72.Bb Theories and models of crystal defects
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
66.30.Lw Diffusion of other defects
71.15.Nc Total energy and cohesive energy calculations
71.15.-m Methods of electronic structure calculations
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Investigation of effective mass of carriers in Bi2Te3̸Sb2Te3 superlattices via electronic structure studies on its component crystals

Guofeng Wang and Tahir Cagin

Appl. Phys. Lett. 89, 152101 (2006); http://dx.doi.org/10.1063/1.2360191 (3 pages) | Cited 7 times

Online Publication Date: 9 October 2006

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The electronic structures of Bi2Te3 and Sb2Te3 were computed and related to the thermoelectric properties of Bi2Te3̸Sb2Te3 superlattices. The authors found that the similarity of the electronic structure of the two materials permits the Bi2Te3̸Sb2Te3 superlattices inherit high band edge degeneracy, and thus have high electrical conductivity. From the calculated effective mass along the superlattice growth direction, we infer that presence of more Sb2Te3 than Bi2Te3 in the superlattice leads to a smaller effective mass and enhanced carrier mobility. Furthermore, our results suggest that external tensile strain parallel to the interface may further improve the thermoelectric performance of the Bi2Te3̸Sb2Te3 superlattices.
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73.21.Cd Superlattices
73.63.-b Electronic transport in nanoscale materials and structures
73.20.At Surface states, band structure, electron density of states
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Fr Low-field transport and mobility; piezoresistance
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
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